Methods and, in particular, microscopes of the species have been known from practical use for some time. In industrial applications, for example in the metrology of line widths or positions on substrates of the semiconductor industry, coordinate measuring instruments such as those described, for example, in German Patent Application DE 198 19 492.7-52 are used. FIG. 3 is a diagram of the measuring instrument in DE 198 19 492.7-52. This measuring instrument serves for highly accurate measurement of the coordinates of features on substrates 8, e.g. masks, wafers, flat screens, and evaporatively deposited features, but in particular for transparent substrates. The coordinates are determined relative to a reference point, to an accuracy of a few nanometers.
In the metrology of line widths or positions on substrates of the semiconductor industry, the detected images are digitally processed in order to extract characteristic measurement parameters. For that purpose, a specimen to be measured—usually a wafer or an exposure mask 8 for manufacturing a wafer—is illuminated with light 13 at a wavelength of 365 nm. The specimen illuminated in this fashion is imaged with an objective of the microscope onto a detector 14, the detector usually being embodied as a CCD camera.
The achievable resolution capability of such an imaging system 10 depends essentially on the light wavelength used and on the numerical aperture of the objective. To increase the resolution capability of the imaging system, the numerical aperture must therefore be increased; there is almost no further possibility for this with present-day microscope objectives, however, since the limits of what is feasible in terms of optics and precision mechanics have largely been reached. The use of short light wavelengths requires the utilization of special optics and optical components, so that here again it is not possible to use light of an arbitrarily short wavelength.